The way points of this bicycle route:
Starting point from edge of Chicago to Green Bay Trail. Howard is the border of Evanston and Chicago here.
Sherman is one way south here, but it's not busy and it beats staying on Custer.
Sherman is one way south for another 1/2 block here. Also, at Oakton there is no stop for cross traffic, so be careful. Oakton doesn't have any lights to use.
What you're going to do here is cross the street, and then head through the plaza on the East side of the railroad tracks.
Ahead of you is the aforementioned plaza. Just go north, it saves you the pain of too crowded streets in downtown Evanston.
You could go left here instead of right and head up Ridge, but it has quite a bit more traffic than the route I chose. It is, however, shorter. On the way back, though, you'd have to go up the hill on Ridge instead of down. If you take Ridge, just be sure to take the left on Lincoln anyway.
At Central, you've crossed into Wilmette
The signs for the trail should be right here. You can just follow the signs from here on out.